This invention relates to a magnetic recording medium of the analog recording system (to be simply referred to as magnetic recording medium, hereinafter), and more particularly, to a magnetic recording medium capable of high density recording.
In recent years, the increasing demand for high density recording is imposed on advanced magnetic recording media. In the commonly used longitudinal magnetic recording scheme wherein the direction of magnetization is within the plane of recording medium, the recording density cannot be increased beyond a certain level because of repulsion of magnetization of adjoining magnetic domains. A great attention is now drawn to the perpendicular magnetic recording scheme wherein the direction of magnetization is perpendicular to the plane of recording medium so that no repulsion of magnetization occurs. Among known media of the perpendicular recording scheme are those having a deposition type recording layer such as a sputtered Co-Cr film and those having a coating type recording layer such as a coating of magnetic powder like barium ferrite.
In preparing recording layers of the coating type, hexagonal barium ferrite and analogues have been widely used because of ease of perpendicular orientation as disclosed in Japanese patent application Kokai Nos. 57-58240, 57-58246, 57-212623, 58-6526, 58-222446, and 59-96532. It is believed for the perpendicular magnetic recording scheme that the size and size distribution of magnetic particles used, the surface roughness of coating, and various other factors have a significant influence on the degree of perpendicular orientation and the performance of magnetic recording media including noise during recording and reproducing operations. In this regard, various considerations were made in the aforementioned patent publications.
Such improvements are not yet fully satisfactory and there is the need for further improving the magnetic layer as well as the particulate magnetic material itself.